1. Field of the Invention
This invention pertains to a digital switching system, and more particularly to an ATM (Asynchronous Transfer Mode) cell broadcasting system utilized in ATM switches, e.g. for ISDN (Integrated Service Digital Network), which exchange ATM cells representing information having different traffic characteristics such as voices, data and moving images.
2. Description of the Related Art
With the recent widespread use of data communication, publicly switched networks now carry important data, as well as traditional voices, and are required to offer high-quality data transmission and exchange.
As a communication network for serving not only low speed data such as voice data, but also high speed data such as moving images, a broadband ISDN (B-ISDN) has begun to be put into practical use and various interfaces are being standardized. Unlike traditional switching methods, a B-ISDN utilizing an asynchronous transfer mode (ATM) can commonly carry various sorts of information at different speeds, e.g. voice data, moving image data and even continuous information mixed with burst information.
An ATM communication network transmits and exchanges information of different bands divided and housed in fixed-length data units called cells, instead of information divided and housed in variable-length packets used in traditional packet communication. Cells containing channel data are indiscriminately multiplexed, transmitted over optical fibers at high speed, and fast-exchanged by hardware switches. Thus, an ATM communication network can offer flexible services requiring different transmission speeds and makes efficient use of transmission paths.
User information is divided into several pieces according to its length and cells are configured by adding headers, e.g. of a few bytes, to the respective data, e.g. of 32 to 120 bytes, comprising the divided pieces of information. A header contains a virtual channel identifier (VCI) for identifying the originating user of the corresponding data. Thus, user information stored in cells is multiplexed over ATM highways before it is transmitted and exchanged. Switch elements in a switch matrix route cells to their respectively connected output highways, when they are turned on.
That is, a conventional switch matrix enables one-to-one communication by outputting an ATM cell inputted from an input highway to only one of a plurality of output highways. Therefore, there is a problem that it lacks the capacity for one-to-many communication, i.e. from one originator to a plurality of destinations, by outputting an ATM cell inputted from an input highway to a plurality of output highways.